My invention relates generally to an apparatus for the transfer (reading and/or writing) of data with disklike record media such as magnetic disks notably including those of the "fixed" or hard disk variety. More particularly, my invention pertains to a system in such an apparatus for controlling the position of the transducer or head with respect to a multiplicity of concentric annular data tracks on the surface of a disklike record medium. The transducer positioning system of my invention particularly features provisions for preventing the transducer from excessive overrun beyond the boundaries of the data storage zone comprised of the tracks on the disk surface.
A variety of schemes have been suggested and used for positioning a transducer with respect to the data tracks on a hard magnetic disk. Typical of such known schemes are: (1) a servo system with a servo head and a replicated servo surface on the disk; (2) another servo system employing an encoder for the detection of the positional relationship between the transducer and the data tracks; (3) still another servo system wherein the transducer reads addresses prerecorded on individual tracks during track seeking; and (4) an open-loop system with a stepper motor for moving the transducer a distance specified by the number of stepping pulses.
The closed-loop servo systems are generally preferred for the accuracy and quickness with which the transducer can be positioned on any selected track. In such servo positioning of the transducer, the track on which the transducer is currently position must be known at every moment during the progress of track seeking, in order that the transducer may be moved the exact distance between the current and destination tracks. However, should the transducer be moved too fast across the data tracks, the exact detection of the current transducer position would become impossible. The transducer might then overrun the data storage zone and ride onto either of the two guard bands disposed radially inwardly and outwardly of the data storage zone on the disk surface.
Usually, the known transducer positioning mechanisms include mechanical limit stops for preventing the transducer from excessive overrun beyond the boundaries of the data storage zone. Such limit stops represent no truly satisfactory solution to the problem of how to avoid excessive transducer overrun. For, if a very substantial error takes place in the positional control of the transducer during track seeking in the prior art devices, the transducer carrier means has been prone to violently hit either of the limit stops, possibly resulting in the impairment of the transducer or the disk.